Ryujinx/ARMeilleure/Decoders/Optimizations/TailCallRemover.cs
Ficture Seven 2421186d97
Generalize tail continues (#1298)
* Generalize tail continues

* Fix DecodeBasicBlock

`Next` and `Branch` would be null, which is not the state expected by
the branch instructions. They end up branching or falling into a block
which is never populated by the `Translator`. This causes an assert to
be fired when building the CFG.

* Clean up Decode overloads

* Do not synchronize when branching into exit block

If we're branching into an exit block, that exit block will tail
continue into another translation which already has a synchronization.

* Remove A32 predicate tail continue

If `block` is not an exit block then the `block.Next` must exist (as
per the last instruction of `block`).

* Throw if decoded 0 blocks

Address gdkchan's feedback

* Rebuild block list instead of setting to null

Address gdkchan's feedback
2020-06-18 13:37:21 +10:00

89 lines
2.9 KiB
C#

using System;
using System.Collections.Generic;
namespace ARMeilleure.Decoders.Optimizations
{
static class TailCallRemover
{
public static Block[] RunPass(ulong entryAddress, List<Block> blocks)
{
// Detect tail calls:
// - Assume this function spans the space covered by contiguous code blocks surrounding the entry address.
// - A jump to an area outside this contiguous region will be treated as an exit block.
// - Include a small allowance for jumps outside the contiguous range.
if (!Decoder.BinarySearch(blocks, entryAddress, out int entryBlockId))
{
throw new InvalidOperationException("Function entry point is not contained in a block.");
}
const ulong allowance = 4;
Block entryBlock = blocks[entryBlockId];
Block startBlock = entryBlock;
Block endBlock = entryBlock;
int startBlockIndex = entryBlockId;
int endBlockIndex = entryBlockId;
for (int i = entryBlockId + 1; i < blocks.Count; i++) // Search forwards.
{
Block block = blocks[i];
if (endBlock.EndAddress < block.Address - allowance)
{
break; // End of contiguous function.
}
endBlock = block;
endBlockIndex = i;
}
for (int i = entryBlockId - 1; i >= 0; i--) // Search backwards.
{
Block block = blocks[i];
if (startBlock.Address > block.EndAddress + allowance)
{
break; // End of contiguous function.
}
startBlock = block;
startBlockIndex = i;
}
if (startBlockIndex == 0 && endBlockIndex == blocks.Count - 1)
{
return blocks.ToArray(); // Nothing to do here.
}
// Mark branches outside of contiguous region as exit blocks.
for (int i = startBlockIndex; i <= endBlockIndex; i++)
{
Block block = blocks[i];
if (block.Branch != null && (block.Branch.Address > endBlock.EndAddress || block.Branch.EndAddress < startBlock.Address))
{
block.Branch.Exit = true;
block.Branch.TailCall = true;
}
}
var newBlocks = new List<Block>(blocks.Count);
// Finally, rebuild decoded block list, ignoring blocks outside the contiguous range.
for (int i = 0; i < blocks.Count; i++)
{
Block block = blocks[i];
if (block.Exit || (i >= startBlockIndex && i <= endBlockIndex))
{
newBlocks.Add(block);
}
}
return newBlocks.ToArray();
}
}
}